In the field of information display, organic EL devices have been highlighted as displaying devices of the forthcoming generation. Hitherto, cathode-ray tubes have been predominantly used in information displaying equipment of larger sizes such as computer termini and TV receivers: However, cathode-ray tubes are large in volume and weight and high in operation voltage, and these may restrict their application in equipment which are directed to use at home, as well as in compact equipment where portability is one of important factors. More required are information displaying equipments which are in a thinner and lighter panel form and operable with a lower voltage and less power consumption. Liquid crystal devices have been frequently used in various fields because of the merit that they are operable with a low voltage and less power consumption. Liquid crystal devices however have the demerits that one hardly receives a clear information therefrom when he or she views them at an angle outside the specific ranges, as well as that their power consumption is not so small as expected because they usually require backlight. Organic EL device has appeared as information displaying means which may overcome these demerits.
Organic EL device is a class of light-emitting device which utilizes electroluminescence such as fluorescence or phosphorescence: It usually comprises a luminescent layer incorporated with a luminescent compound and inserted between a cathode and anode to which dc voltage is energized to inject holes and electrons in the luminescent layer so that a pair of hole and electron recouple each other to make in the luminescent compound an excited state which subsequently returns to the ground state to emit such luminescence. Organic EL device is characterized in that its luminescent color tint can be controlled to a desired level by selecting an appropriate organic compound to be used as host compound in the formation of luminescent layer, and screening guest compounds (or dopants) which may match with the host compound. This may remarkably increase the brightness and life expectancy for luminescence in organic EL device, dependently upon the combination of host and guest compounds. Organic EL device has been deemed to be in principle an excellent device because of the merit that it does realize an autonomous light emission and this would advantageously save power consumption.
Many of organic EL devices proposed hitherto however have the disadvantage that they are low in durability, and therefore their brightness decreases within a short period of time when used under severe conditions, for example, in case of equipping them to automobiles where mechanical vibrations and high temperatures are unavoidable.
In view of such situation, the objectives of this invention are to provide a luminescence-assisting agent which would be useful even in highly durable organic EL devices, as well as to provide its uses.